Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular brush seal includes an annular backing plate which may terminate in the shape of an annular labyrinth-seal tooth having a sloped downstream-facing surface and also includes bristles which are canted at typically a forty-five degree angle with respect to a radius line. A gas or steam turbine brush seal is made up of circumferentially-arrayed and radially-cut brush seal segments. The angled bristles create an exposed area at one circumferential edge of each segment. The labyrinth-seal tooth reduces leakage through this exposed area. Unfortunately, Applicants have found that radial contact of the labyrinth-seal tooth with the rotor during startup deformed the annular tooth into large circumferential areas of bristles preventing recovery of these bristles once the rotor reached steady-state operating conditions. The unrecovered bristles allowed large leakage.